The present invention relates to a method and apparatus for cutting discrete quantities of molten plastic material from a supply of molten plastic material for subsequent compression molding of the plastic material into plastic articles. More particularly, the invention relates to a plurality of cutters which rotate relative to a plurality of molten plastic delivery nozzles to cut pellets of molten plastic from the nozzles and to carry the thus cut pellets of molten plastic into cavities for compression molding articles.
U.S. Pat. No. 4,277,431, to Peller, hereby incorporated by reference, discloses an apparatus for cutting discrete quantities or pellets of molten plastic material for subsequent placement in respective mold cavities. This apparatus is particularly suited for use in the manufacture of closures by compression molding, including the formation of compression molded closure shells, and the formation of compression molded liners within associated closure shells. U.S. Pat. Nos. 4,343,754 to Wilde et al., and 4,497,765 to Wilde et al., both hereby incorporated by reference, disclose compression molding of threaded, tamper-indicating plastic closures, and compression molding of liners in such closures, for which manufacturing processes the apparatus of the above U.S. Pat. No. 4,277,431 is suited for use.
The apparatus of U.S. Pat. No. 4,277,431 includes a nozzle through which molten plastic material is delivered from an associated extruder or the like, and a rotatably driven cutting blade which is rotated with respect to the nozzle. As plastic is extruded from the nozzle, a discrete quantity or pellet of plastic material is cut during each rotation of the associated cutting blade. Immediately thereafter, the severed plastic pellet is moved from the face of the nozzle by the cutting blade for delivery to a respective mold cavity. The mold cavity may comprise either a female mold die for formation of a closure shell by compression molding, or a closure shell within which the molten plastic is compression molded for formation of a sealing liner.
The cutter apparatus of U.S. Pat. No. 4,227,431 is configured to facilitate separation of each plastic pellet from the cutting blade by creating a slight mechanical interference between the cutting blade and the face of the associated nozzle. Thus, as the cutting blade rotates with respect to the nozzle, the blade is flexed or deflected as it engages the nozzle face and severs the extruded plastic material. As the blade continues to rotate, with the severed plastic material carried on the flexed surface of the cutting blade, the cutting blade disengages the face of the nozzle, thereby rapidly accelerating the pellet to facilitate its separation from the blade and delivery of the pellet to one of the associated cavities. This cutting and subsequent xe2x80x9cflickingxe2x80x9d like action of the cutting blade is sometimes referred to as the xe2x80x9ccut-and-flipxe2x80x9d portion of each cutting cycle.
The above patent contemplates that the disclosed cutting apparatus be mechanically-driven from the associated molding apparatus, thus effecting the desired synchronous operation of the cutter. However, it will be appreciated that increases or decreases in production speed necessarily result in corresponding variation in the xe2x80x9ccut-and-flipxe2x80x9d portion of the cutting cycle, which can create undesirable variability in the speed, direction, rotational velocity, and orientation of the plastic pellet as it is delivered to the associated cavity. This can, in turn, create problems regarding pellet placement, orientation, and an undesirable tendency of the pellet to bounce upon delivery into the associated cavity.
U.S. Pat. No. 5,596,251 describes a cutter apparatus driven by a servo motor, the operation of which is coordinated with an associated rotary carousel on which cavities are successively presented to the cutter apparatus. In order to effect separation of each discrete quantity of plastic material from the cutting blade of the cutter apparatus, the servo motor is operated to create a period of distinct deceleration during each rotary cutting cycle, thereby separating the molten plastic from the surface of the cutting blade.
The cutter apparatus disclosed in each of the aforementioned patents includes a single rotating cutter which cuts and disperses a single pellet during each rotation. The throughput of such apparatus is thus limited by the rotational speed of the single cutter. To increase the overall throughput of the compression molding apparatus requires additional cutter apparatuses and associated carousels which requires costly additional factory floor space.
The present inventors have recognized that it would be desirable to provide a cutter apparatus for cutting molten plastic pellets from a source of molten plastic material and delivering the pellets into successive cavities for subsequent compression molding which could be effectively operated at a high rate of speed to produce a high rate of molded articles. The apparatus desirably would reliably operate to produce a high percentage of flawlessly molded articles. The apparatus desirably would require a minimum of factory floor space.
The present invention is directed to a plastic pellet cutting and delivery system particularly suited for use in compression molding of plastic closure shells, and plastic liners in closure shells. The present invention includes a high throughput compression molding apparatus having a rotatable bank of cutters operatively associated with a bank of molten plastic delivery nozzles. Also, the invention includes a plurality of molding blocks, each block having a row of molding cavities for successively receiving a row of plastic pellets cut by the bank of cutters from the bank of molten plastic delivery nozzles. The molding blocks are advantageously carried on a revolving carousel.
A compression molding device such as disclosed in U.S. Pat. Nos. 4,343,754 or 4,497,765 can be used to mold the plastic pellets carried by the blocks into articles, such as threaded, tamper-indicating plastic closures or liners for closures.
The present system is used in conjunction with a rotary compression molding apparatus, which typically includes a rotating carousel or turret which carries cavities in the form of mold dies or closure shells. According to the present invention, the carousel circulates molding blocks having radially arranged rows of cavities. The present system effects delivery of plural discrete quantities of molten plastic material (i.e., plastic pellets) to the rows of circulating cavities by the provision of an extruder or like apparatus which provides a source of molten plastic material, and a plurality of the cutting blades driven with respect to nozzles flow connected to the extruder. Upon rotation of the blades, the blades cut the plurality of pellets of plastic material as it is being extruded from the nozzles. A precision servo motor drives the cutter shaft via a toothed timing belt and pulley arrangement.
The present invention incorporates a multi-cutter comprising a plurality of cutter assemblies mounted on a cutter shaft, the cutter shaft being rotated about its axis by a servo motor. The cutter assembly can be as described in U.S. application Ser. No. 09/444,936, filed on the same day as the present application, and identified by attorney docket number HCI0467P00480US, and entitled: xe2x80x9cRotary Cutter For Cutting, Measuring, and Dispensing Molten Plastic,xe2x80x9d herein incorporated by reference.
Each such cutter assembly comprises a cutter body which is held substantially within a radial bore formed in an end portion of a cutter shaft, and a protruding cutter head extending from the cutter body. The cutter shaft includes one or more internal air passages for pressurized air delivery to each of the cutter bodies. Each cutter assembly can include a plunger which reciprocates adjacent to the cutter head to displace a plastic pellet held by the cutter head. Each cutter body can include a series of air apertures directed toward an internal region of the respective cutter head for passing pressurized air into the cutter head to dislodge a plastic pellet held thereby. The air apertures are in flow communication with one of the internal air passages within the cutter shaft. Internal cooling fluid channels through the cutter shaft are in flow communication with an annular area between each cutter body and an inside wall of the respective radial bore of the cutter shaft for maintaining the cutter bodies at a desired temperature during operation.
The cutter shaft is rotated within a rotary union block. The cutter shaft includes one or more first annular channels around its circumference in flow communication with the internal air passages. The cutter shaft also includes second and third annular channels around its circumference and in flow communication with the two internal cooling channels respectively. The rotary union block includes corresponding channels or passages in flow communication with the first, second and third annular channels of the cutter shaft, such that pressurized air and cooling water can be sealingly transferred between the rotary union block and the cutter shaft given that the cutter shaft is rotating and the union block is stationary.
The bank of extrusion nozzles receive flow of molten plastic from a manifold assembly. The manifold assembly includes an inlet adapter, open into a first cross shaped or xe2x80x9cclover leafxe2x80x9d shaped block manifold which separates the flow into four divergent flow paths. The four flow paths each connect to one of four volumetric metering or proportioning pumps. The volumetric metering pumps are used to provide consistent volume flow and pressure of the molten plastic. The pumps are each connected at outlets thereof to a second cross shaped or xe2x80x9cclover leafxe2x80x9d shaped block manifold. The second manifold includes channels that direct the four flow paths into four adjacent outlets. The four outlets are connected by tubes, such as hot runners, to a right angle or L-shaped manifold block. The right angle manifold block is connected to a bank of nozzles. The first and second manifolds, the tubes, and the right angle manifold block are all heated and insulated to maintain the molten plastic at a precise and controllable temperature.
The manifold assembly thus cooperates with the bank of delivery nozzles to deliver a controlled flow of molten plastic to the nozzles. The bank of rotary cutters are arranged to cooperate with the bank of delivery nozzles to separate rows of pellets of molten plastic extruded from the nozzles and to dispense the rows of pellets into successively presented molding blocks each having a row of cavities, for subsequent compression molding into articles. According to the invention, a greatly increased throughput of plastic pellets deposited into molding cavities for compression molding is achieved without substantially increasing a floor space requirement for the compression molding apparatus.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.